Method for controlling clutch of vehicle

ABSTRACT

A method for controlling a clutch includes judging whether or not a slip amount of the clutch is reduced to below a first reference value by a controller after starting of the vehicle is launched, judging whether or not accumulated slip energy of the clutch until a present time from the launch of starting the vehicle is a second reference value or more, as a result of judgment as to the slip amount of the clutch, if the slip amount of the clutch is below the first reference value, and controlling engagement of the clutch so as to prevent overheating of the clutch while the controller causes an engine to maintain a target engine speed, as a result of the judgment as to the accumulated slip energy, if the accumulated slip energy is the second reference value or more.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean PatentApplication No. 10-2015-0145798, filed on Oct. 20, 2015 with the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to a method for controlling a clutch of avehicle, and more particularly to a method for controlling a dry clutchof a vehicle loaded with an Automated Manual Transmission (AMT) or aDual-Clutch Transmission (DCT) using the clutch when the vehicle isstarted.

BACKGROUND

In general, in an AMT or DCT vehicle using a dry clutch, the clutch mayoverheat due to continuous slip. Overheating of the clutch may cause achange of characteristics of the clutch and, in some cases, may cause anadverse situation if the clutch is released due to a temporary loss offriction of a clutch disc facing. Since an improvement ofcharacteristics of the facing can be difficult, it is important tocontrol the clutch so as not to cause overheating of the clutch.

Hereinafter, for reference, the term “clutch” means a “dry clutch”unless stated otherwise.

In general, as a slip amount of a clutch increases, a heat generationrate increases. Therefore, when a slip amount of the clutch is reduced,the heat generation rate is decreased. However, if the clutch isconnected to a power source, such as an engine or a motor, so as torapidly reduce the slip amount of the clutch, an impact can be caused.Therefore, in terms of drivability of a vehicle, if a soft feeling needsto be achieved as in starting of a torque converter-type automatictransmission, a method of slowly reducing the slip amount of a clutch isused.

However, if the slip amount of the clutch is slowly reduced on a slopedroad, a heat generation rate is greatly increased. Since a presence of aslope corresponds to an increase in a vehicle load, acceleration of thevehicle is decreased and thus the slip amount is more slowly reduced.Consequently, an excessive heat generation rate can result.

The above description has been provided to aid in understanding of thebackground of the present disclosure and should not be interpreted asconventional technology known to those skilled in the art.

SUMMARY OF THE DISCLOSURE

Therefore, the present disclosure has been made in view of the aboveproblems, and it is an object of the present disclosure to provide amethod for controlling a clutch of a vehicle in which slip of the clutchis slowly reduced within the limit not causing overheating of the clutchso that generation of impact during starting of the vehicle isprevented, and overheating of the clutch is prevented by rapidlyreducing slip of the clutch in a situation in which an excessive amountof heat is generated in the clutch, so as to assure stability of thevehicle and to improve durability of the clutch.

In accordance with the present disclosure, the above and other objectscan be accomplished by the provision of a method for controlling aclutch of a vehicle, the method including judging whether or not a slipamount of the clutch is reduced to be below a first reference valuethrough a controller after starting of the vehicle is launched, judgingwhether or not accumulated slip energy of the clutch until now, or apresent time, from launch of starting of the vehicle is a secondreference value or more through the controller, as a result of judgmentas to the slip amount of the clutch, if the slip amount of the clutch isbelow the first reference value, and controlling engagement of theclutch through the controller so as to prevent overheating of the clutchwhile the controller causes an engine to maintain a target engine speed,as a result of judgment as to the accumulated slip energy, if theaccumulated slip energy is the second reference value or more.

Prior to execution of judgment as to the slip amount of the clutch afterstarting of the vehicle is launched, the controller may set the targetengine speed according to the manipulated quantity of an accelerationpedal by a driver, and execute feedback control of the clutch so thatthe speed of the engine follows the target engine speed until therequirements of judgment as to the slip amount of the clutch aresatisfied.

As a result of judgment as to the accumulated slip energy, if theaccumulated slip energy is below the second reference value, thecontroller may control engagement of the clutch according to a targetslip reduction rate set to prevent impact generated by engagement of theclutch.

Control of engagement of the clutch according to the target slipreduction rate set to prevent impact may continue to be executed untilengagement of the clutch has been completed.

Control of engagement of the clutch so as to prevent overheating of theclutch may continue to be executed until engagement of the clutch hasbeen completed.

The accumulated slip energy of the clutch may be acquired byaccumulating a value, acquired by multiplying torque of the clutch bythe slip amount of the clutch, from a point of time when starting of thevehicle is launched.

The torque of the clutch may be calculated by a torque observer toreceive torque and speed of the engine and thus to estimate the torqueof the clutch and the slip amount of the clutch may be calculated as adifference between the speed of the engine and the speed of an inputshaft of a transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a flowchart illustrating a method for controlling a clutch ofa vehicle in accordance with one embodiment of the present disclosure;

FIG. 2 is a block diagram illustrating the method of FIG. 1 inaccordance with an embodiment of the present disclosure;

FIG. 3 is a graph illustrating an execution of prevention of overheatingin accordance with an embodiment of the present disclosure;

FIG. 4 is a graph illustrating an execution of prevention of an impactin accordance with an embodiment of the present disclosure; and

FIG. 5 is a view illustrating a configuration of a DCT to which anembodiment of the present disclosure is applicable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

With reference to FIGS. 1 to 4, a method for controlling a clutch of avehicle in accordance with one embodiment of the present disclosure mayinclude judging whether or not a slip amount of the clutch is reduced tobe below a first reference value through a controller after starting ofthe vehicle is launched or initiated (Operation S10), judging whether ornot accumulated slip energy of the clutch until now, or a present time,from launch of starting of the vehicle is a second reference value ormore through, or using, the controller, as a result of the judgment asto the slip amount of the clutch, if the slip amount of the clutch isbelow the first reference value (Operation S20), and controlling anengagement of the clutch through the controller so as to preventoverheating of the clutch while the controller causes an engine tomaintain a target engine speed, as a result of judgment as to theaccumulated slip energy, if the accumulated slip energy is the secondreference value or more (Operation S30).

That is, in an embodiment of the method in accordance with the presentdisclosure, slip energy accumulated in the clutch due to slipping of theclutch during starting of the vehicle is judged and, if there is apossibility of overheating the clutch, the clutch is rapidly engagedalthough impact is applied to the vehicle, thereby suppressingadditional slip of the clutch and consequently preventing overheating ofthe clutch.

Of course, if the slip energy accumulated in the clutch during startingof the vehicle is not high and there is no possibility of overheatingthe clutch, Operation S40, which will be described later, may beexecuted to prevent an impact to the vehicle and to promote a smoothengagement of the clutch.

Therefore, in accordance with the present disclosure, in a situation inwhich there is no possibility of overheating the clutch, the clutch canbe smoothly engaged to prevent an impact applied to the vehicle and, ina situation in which there is a possibility of overheating the clutch,slip of the clutch is rapidly reduced to prevent overheating of theclutch, thereby assuring stability of the vehicle and improvingdurability of the clutch.

In this embodiment, prior to execution of Operation S10 after a startingof the vehicle is launched, or initiated, the controller sets the targetengine speed according to the manipulated quantity of an accelerationpedal by a driver and executes a feedback control of the clutch so thatthe speed of the engine follows the target engine speed until therequirements of Operation S10 are satisfied.

That is, when the driver presses the acceleration pedal and thusstarting of the vehicle is launched, the controller may select a targetengine speed corresponding to a manipulated quantity of the accelerationpedal by the driver from a target engine speed map and may executefeedback control of the clutch so that the speed of the engine followsthe target engine speed. Such a target engine speed may be substantiallyequal to the target engine speed used in Operation S30.

For example, the manipulated quantity of the acceleration pedal may be asignal value from an acceleration position sensor (APS).

Further, feedback control of the clutch substantially refers to controlof torque transmitted to the clutch by repetitively controlling a clutchactuator by the controller, and such feedback control may be executedthrough a conventional feedback control method, such as ProportionalIntegral (PI) control or Proportional Integral Derivative (PID) control.

As a result of a judgment as to the accumulated slip energy (OperationS20), if the accumulated slip energy is below the second referencevalue, the controller may control engagement of the clutch according toa target slip reduction rate set to prevent impact generated by anengagement of the clutch (Operation S40).

That is, in one case, although the clutch may slip more, there is nopossibility of overheating the clutch and thus generation of impact onthe vehicle may be prevented and a sense of smooth starting of thevehicle may be assured through smooth clutch engagement.

Operation S40 and Operation S30 may continue to be executed untilengagement of the clutch has been completed, thereby finishing astarting of the vehicle.

Here, the first reference value used in Operation S10 may be defined asa slip amount of the clutch that is enough to confirm whether or notstarting of the vehicle is almost completed and the vehicle reaches thelast stage of starting. In consideration of purposes of the presentdisclosure, in Operation S30, the speed of the engine is not increasedslightly above the target engine speed so that the clutch is engagedwhile slip of the clutch is gradually reduced, but the speed of theengine may continuously follow the target engine speed and the clutchmay be engaged so that the slip amount of the clutch is rapidly reducedand thus determined to be within a range within which a generated impactis reasonably tolerated so as to prevent overheating of the clutch.

For example, the first reference value may be set to be below 100 RPM,i.e., a level at which starting of the vehicle will be completed soon.

The accumulated slip energy of the clutch may be acquired byaccumulating a value, acquired by multiplying torque of the clutch bythe slip amount of the clutch, from a point of time when starting of thevehicle is launched. The second reference value with which theaccumulated slip energy is compared may be set based on, if the clutchcontinues to slip, whether or not there is a possibility of overheatingthe clutch to have a negative influence on the clutch, in considerationof purposes of the present disclosure.

Therefore, the second reference value may be set to be a level at whicha possibility of overheating the clutch begins to show through manystarting tests and analyses.

With reference to FIG. 2, a torque of the clutch may be calculated by atorque observer which receives a torque and a speed of the engine andthus estimates a torque of the clutch, and the slip amount of the clutchmay be calculated as a difference between the speed of the engine andthe speed of an input shaft of the transmission.

FIG. 3 is a graph illustrating a speed Ne of the engine, a speed Ni ofthe input shaft of the transmission, an acceleration G of the vehicle,and accumulated slip energy according to a time lapse if prevention ofoverheating (Operation S30) is executed. When the vehicle is started,the speed of the engine may follow the target engine speed, the clutchmay be engaged while slipping, the speed of the input shaft of thetransmission may reach the speed of the engine, and, upon judging thatthe slip amount of the clutch is below the first reference value at timeA, judgment as to accumulated slip energy (Operation S20) may beexecuted. Here, since the accumulated slip energy may already exceed thesecond reference value, prevention of overheating (Operation S30) may beexecuted, the clutch may be immediately engaged by controlling theclutch so that the engine maintains the target engine speed and, thus,the speed of the input shaft of the transmission is rapidly synchronizedwith the speed of the engine. By immediately engaging the clutch, theacceleration of the vehicle is changed and, thus, impact may begenerated.

FIG. 4 is a graph illustrating an execution of prevention of impact(Operation S40). Such a graph illustrates a situation in which, sincethe accumulated slip energy at a point of time A is below the secondreference value, slip of the clutch is slowly reduced according to atarget slip reduction rate and thus starting of the vehicle is completedwithout generation of impact.

Therefore, the target slip reduction rate may be set to be a level, atwhich an impact of the vehicle is not generated and smooth starting ofthe vehicle is completed during starting, through many tests andanalyses.

For reference, FIG. 5 is a view illustrating a configuration of a DCT towhich the present disclosure may be applicable. Power of an engine E maybe supplied to driving wheels W through a dual clutch transmission(DCT). Two clutches 1 of the DCT are respectively controlled by clutchactuators 3, the clutch actuators 3 are controlled by a controller 5,and the controller 5 receives a signal from an accelerator positionsensor (APS) 7 to receive the manipulated quantity of an accelerationpedal.

The controller 5 may be configured to provide information, such astorque and speed of the engine E, etc.

As is apparent from the above description, in a method for controlling aclutch of a vehicle in accordance with one embodiment of the presentdisclosure, slip of the clutch is slowly reduced within the limit notcausing overheating of the clutch so that impact is not generated duringstarting of the vehicle. Overheating of the clutch is prevented byrapidly reducing slip of the clutch in a situation in which an excessiveamount of heat is generated in the clutch, thereby assuring stability ofthe vehicle and improving a durability of the clutch.

Although the preferred embodiments of the present disclosure have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the disclosureas disclosed in the accompanying claims.

What is claimed is:
 1. A method for controlling a clutch of a vehiclecomprising: judging whether or not a slip amount of the clutch isreduced to below a first reference value by a controller after startingof the vehicle is launched; judging whether or not accumulated slipenergy of the clutch until a present time from the launch of startingthe vehicle is a second reference value or more through the controller,as a result of judgment as to the slip amount of the clutch, if the slipamount of the clutch is below the first reference value; and controllingengagement of the clutch through the controller so as to preventoverheating of the clutch while the controller causes an engine tomaintain a target engine speed, as a result of the judgment as to theaccumulated slip energy, if the accumulated slip energy is the secondreference value or more.
 2. The method according to claim 1, wherein,prior to the step of judgment as to the slip amount of the clutch afterstarting of the vehicle is launched, the controller sets the targetengine speed according to the manipulated quantity of an accelerationpedal by a driver, and executes feedback control of the clutch so thatthe speed of the engine follows the target engine speed until therequirements of the judgment as to the slip amount of the clutch aresatisfied.
 3. The method according to claim 1, wherein, as a result ofthe step of judgment as to the accumulated slip energy, if theaccumulated slip energy is below the second reference value, thecontroller controls engagement of the clutch according to a target slipreduction rate set to prevent an impact generated by engagement of theclutch.
 4. The method according to claim 3, wherein control ofengagement of the clutch according to the target slip reduction rate setto prevent impact continues to be executed until engagement of theclutch has been completed.
 5. The method according to claim 1, whereincontrol of engagement of the clutch so as to prevent overheating of theclutch continues to be executed until engagement of the clutch has beencompleted.
 6. The method according to claim 1, wherein the accumulatedslip energy of the clutch is acquired by accumulating a value, acquiredby multiplying torque of the clutch by the slip amount of the clutch,from a point of time when starting of the vehicle is launched.
 7. Themethod according to claim 6, wherein: the torque of the clutch iscalculated by a torque observer that receives a torque and a speed ofthe engine and thus estimates the torque of the clutch; and the slipamount of the clutch is calculated as a difference between the speed ofthe engine and the speed of an input shaft of a transmission.